1. Field of the Invention
The present invention relates to a shampoo composition containing encapsulated or particulated oily substances. Particularly, the shampoo composition of the present invention ensures the homogeneous dispersion and stability of such capsules or particles for long periods and provides excellent conditioning and esthetic effects for the hair.
2. Description of the Prior Art
There are a variety of oily substances known as hair conditioning and esthetic agents, including mineral, animal and plant oils. However, due to their physicochemical properties, such oily substances are inconvenient for general use and application. Once such substances are incorporated into a shampoo, they are not readily applicable to the shampoo system and thus adversely effect the intrinsic performance of the shampoo, rather imparting the desired physical and esthetic properties to the hair.
To solve such problems, encapsulation has been developed in the art. Many prior patents have disclosed methods for producing microcapsules including water insoluble substances therein and hair care compositions containing the microcapsules. For example, Japanese Examined Patent Publication No. (Sho)46-38244 discloses a method of treating a capsule wall membrane such as gelatin with a cross-linking agent such as formaldehyde and glutaraldehyde, followed by drying and heating at a temperature of 120.degree. C. to 150.degree. C. Japanese Unexamined Patent Publication No. (Sho)56-100630 discloses a method of treating an aqueous dispersion containing a capsule having a wall membrane of polyvinyl alcohol with, for example, acids and dialdehydes such as glyoxal and glutaraldehyde; or acids and urea and/or melanine and formaldehyde; or alkali and divinylsulfone and/or methylvinyl ketone; or alkali and epichlorohydrin. Japanese Unexamined Patent Publication No. (Sho)56-100631 discloses a method of treating an aqueous dispersion containing a capsule having a wall membrane of polyvinyl alcohol with an organic titanium compound such as diisopropoxy titanium bisacetyl acetone and aminoalcohol titanium chelate. EP Publication No. 0590538 A1 discloses a transparent leave-on hair treatment composition including capsules of a water insoluble hair-treating compound encased in a shell material such as gelatin or acacia gum. U.S. Pat. No. 5,185,155 discloses a process for producing capsules containing a hydrophobic material with the use of silica particles whose size are all not greater than 100 nm. U.S. Pat. No. 4,115,315 discloses a process for producing capsules having pearlescent properties by the incorporation of pearlescent particles in the capsule walls thereof. U.S. Pat. No. 3,607,775 discloses minute capsules having walls which comprise a complex of at least two polymeric materials originally having opposite net electrical charges, with at least one of these polymeric materials being autogenously polymerizable to a solid polymeric material insoluble in the manufacturing vehicle. EP Publication No. 0332175 A2 discloses a method of producing a microcapsule capable of protecting a core substance by completly blocking a permeation of foreign materials, and having a high safety factor with respect to the human body.
As described above, most prior techniques for encapsulation do not cover aspects for keeping capsules homogenously and stably dispersed in the shampoo compositions.
For shampoo compositions containing encapsulated oily substances produced according to the aformentioned prior techniques, our experiments revealed that capsules in the diameter of about 0.3 mm or more floated on the upper phase of the shampoo system or precipitated to the bottom of the shampoo system. Moreover, some of capsules ruptured which lead to the release of oily substances into the shampoo system, which resulted in a considerable reduction of conditioning and esthetic properties.
There are few exemplary patents relating to techniques for the dispersion of particles having diameters of approximately 10 .mu.m or less, for examples, U.S. Pat. Nos. 4,854,333 or 4,345,080, EP Publication Nos. 0285388, 0312234 or 0422508, and UK Patent No. 2187197. However, upon our examination of shampoo compositions produced as disclosed in such patents, we found that capsules containing oily substances were unsatisfactorily dispersed in the shampoo systems. Specifically, using the patented techniques, it was impossible to stably disperse capsules containing oily substances, with the specific gravity of the capsules being 0.5-0.95 at 25.degree. C., into the shampoo systems.
Accordingly, the object of the present invention is to solve the above described problems and to provide an improved shampoo composition in which capsules containing oily substances are stably dispersed for a long period. The inventors developed a new shampoo system which ensures satisfactorily endured dispersion and stability of capsules containing oily substances therein.